I just realized the the check engine light doesn't come on when I turn the key forward, like the other lights do (abs, battery, etc). I just bought the truck a few days ago. It might be the bulb, but how do I check to see if it was disabled by the previous owner, etc? Also the dash illumination light (so you can see the dash at night) isn't coming on either. I guess I should have checked this truck out a bit better before I bought it, but it's mine now, so any tips how to approach both these issues would be much appreciated.

 

The CEL(Ford calls it a MIL, malfunction light) bulb gets 12volts with key on and then Computer controls the Ground for the bulb, and computer should ground it as it boots up.

The dash lights are grounded all the time and get 12volts, or less, from the Dimming module WHEN the light switch is ON.

You should probably pull out the instrument cluster and have new bulbs at the ready

Diagram is below

C216 Pin 9 pink wire, is the GROUND for the CEL, it comes from pin 2 on the computer(PCM)
You can test it with volt or ohm meter to see if that wire is a GROUND when key is turned on, it doesn't stay a Ground forever just while computer boots up.
C214 pin 13 is the 12volts for the CEL bulb but also for most of the gauges and indicator lights, so probably not a fuse issue

Dash lights
And then test for voltage on C215 pin 4 and C214 pin 8 with light switch on, key doesn't have to be on, there are 3 bulbs on each "leg"
Rotate dimmer to see voltage change

 

Great info, I appreciate it. So far I've pulled the cluster and found two of the illumination bulbs blown, the check engine bulb blown, and the fuel reset is bulb/retainer is completely missing. So, two of the four illuminations bulbs are blown. I haven't checked the diagram out and actually read this post after already pulling the cluster. Are the illumination lights in series like old school Christmas bulbs? If not I have other issues with the illumination light circuit. Going to dive in a bit more into what you have listed stated above and check out the attached diagram. And, call the local parts store to see if I can get the bulbs I need and hopefully a bulb retainer for the fuel rest...

Update - So, I got side tracked trying to track down bulbs. The 161's or 194's for the illumination are pretty common still. However, the mini bulbs for the check engine, ABS, etc not so easy. The bulbs have NH6 37G printed on them. None of the local part stores have them. Called Ford, who said they could get two at 13 bucks each and didn't have the part number for the bulb so I could try to find them. The fun, the fun...

 

https://www.bulbtown.com/37_Miniatur..._Base_p/37.htm

pretty sure its a #37 bulb - measure and compare to that link.

 

Also just replace all the illumination bulbs - they all have the same amount of life on them and are all nearing the end. Save the good used ones for places where they are easier to access (license plate lights, front parking corner lights , etc)

 

Thanks for the info guys. I ran down to Advance Auto Parts about a mile from the house and bought just enough bulbs to test things. If it works I'll go only line and buy a bunch for the 194's and 37's to replace all the bulbs in the cluster. Good idea on using the old 194's for other areas like the dome lights, etc. I'll put it back tomorrow and report back.

This is a bit off topic, but my 3rd light and dome light wasn't working - that was a fuse. The 3rd brake light was still not working - that was the bulb. The dome lights were staying on all the time - I fixed that by removing the plastic stop pin that keeps the sliding switch from popping all the way out of it's track - then I bent the contact tabs on the the sliding switch out some for better/stronger contact - works now like it's supposed to now. I don't know if it's the norm or not, but my fuse box is missing the following numbered fuses: 23,30,31,32,34,35,36.

For the Fuel Reset light, the one missing the #37 twist socket, I was thinking maybe I could just solder the bulb in place (if I can't locate the small #37 twist socket).

 

Thanks for the info guys. I ran down to Advance Auto Parts about a mile from the house and bought just enough bulbs to test things. If it works I'll go only line and buy a bunch for the 194's and 37's to replace all the bulbs in the cluster. Good idea on using the old 194's for other areas like the dome lights, etc. I'll put it back tomorrow and report back.
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This is a bit off topic, but my 3rd light and dome light wasn't working - that was a fuse. The 3rd brake light was still not working - that was the bulb. The dome lights were staying on all the time - I fixed that by removing the plastic stop pin that keeps the sliding switch from popping all the way out of it's track - then I bent the contact tabs on the the sliding switch out some for better/stronger contact - works now like it's supposed to now. I don't know if it's the norm or not, but my fuse box is missing the following numbered fuses: 23,30,31,32,34,35,36.

For the Fuel Reset light, the one missing the #37 twist socket, I was thinking maybe I could just solder the bulb in place (if I can't locate the small #37 twist socket).
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Update - reporting back

I got up early to test the cluster and try to beat the Florida heat before it kicks in and both the illumiantion lights and the check engine light is working. And, the check engine light goes out after starting - which is good as you never know.

The two pack of standard #194 bulbs I purchased fit/work just fine for the illumination lights.
The two pack of standard #37 bulbs I purchased fit/work just fine for the check engine, abs, etc lights.

I will most like use the link provided above by Dngr Rnger (https://www.bulbtown.com/37_Miniatur..._Base_p/37.htm) to purchase a complete set of new #194 and #37 bulbs and use the old ones as spares. And, will mount just enough back in place so I can use the truck while waiting on the bulbs. Who ever got into the dash before I did had paper, glue, etc in there to get everything to stay in place - I can only assume they were a bit too aggressive when removing it - a testament to go slow and gentle with these things. So, I will use the time it takes for delivery of the bulbs to also try and repair the broken connections (if I can).

Which brings me to another question. Has anyone removed the protective clear lens before? It's got unwanted extra goodies (dirt, etc) in there I'd like to clean out while I have it out of the dash - but the lens appears to be heat sealed on (unless it's just stuck due to time).

Thanks again for the help. I'm trying add/document stuff here that might help someone else...
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Remove clear plastic lens update
So, I figured this one out here real quick. The clear lens is permanently attached to the bezel and will come off with the bezel if you remove all the bezel screws. No other issues appeared when I did this (gauges falling out, etc). So, I'm off to clean up my cluster some and do a temp installation and order some bulbs...
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Good work

Thanks for the update and fixes